A well known mechanical device for measuring torque applied to a fastener comprises a scale mounted on the shaft of a torque wrench to indicate the angular deflection of the shaft. The very limited accuracy of this mechanical device makes it unsuitable for applications requiring great precision and care in applying torque.
Increased accuracy may be achieved by electronic means for sensing and displaying applied torque. One such device is disclosed in the U.S. Pat. No. 3,895,517 to Otto. The Otto device includes strain-sensitive variable resistors mounted on the neck of an elongated torque wrench handle to measure bending strain in the handle as torque is applied. The resistors are connected into a bridge. The unbalance signal therefrom is digitized using a clock circuit, decoded and displayed. The clock, decoders and display circuitry are all carried within the handle of the Otto device, although the disclosure of the specific mounting structure is very vague.